This invention relates to sealing of the annulus between a tubing hanger and a surrounding spool such as an xmas tree, in a wellhead assembly having a laterally extending fluid conduit. For example, the laterally extending conduit may comprise the production outlet of a horizontal xmas tree.
There is a trend towards subsea completions incorporating increasingly large bores. Current subsea xmas tree system configurations (both parallel and concentric) can be inefficient in terms of space usage within the tubing hanger assembly. For large bore systems it would be advantageous to reconfigure the subsea xmas tree system whilst maintaining a large number of down-hole lines through the tubing hanger. A solution for releasing additional radial space to facilitate larger bores would be to reduce the size of the mechanism for sealing off the annulus void.
The design of large bore subsea xmas tree s and completions is constrained due to requirement s of utilizing existing standard BOP configurations. Therefore in order to run larger completion tubing, space must be saved elsewhere to permit using existing BOP""s. Additionally, particularly in the case of deepwater developments, significant cost savings can be achieved by using smaller standard BOP and casing programs while still maintainingxe2x80x94or increasingxe2x80x94the radial space available for the completion tubing. In this way vessel selection is made easier, and hence costs decreased, due to smaller handling requirements associated with the smaller BOP size.
The problematic situation of a drive toward larger bore completions coupled with potentially utilizing smaller BOP stacks makes the radial space taken within the well system for annular packoffs of prime importance. Any space saved here can have a direct impact on the size of the completion tubing that can be accommodated.
Essentially, the sealing requirement for a slick bore tubing hanger is to seal the annulus between the tubing hanger and spool (wellhead, xmas tree or tubing spool), maintaining a clearance while running in the hanger, and once the hanger is in position, setting the seal to a sealed condition. In the particular case of horizontal production outlet tubing hangers, it is usual to seal the annulus above and below the horizontal outlet. In the case of conventional tubing hangers (or casing hangers), only one seal barrier is required to seal off the annulus.
The present invention aims to release additional space in a tubing hanger and wellhead system incorporating a lateral wellbore fluid conduit by improving the mechanism for sealing off the annulus void. In this way, larger bore completion tubing can be accommodated. Accordingly the present invention provides a wellhead system comprising a wellbore fluid conduit extending laterally between a tubing hanger and a surrounding spool in use, the system comprising a sleeve slideable axially of the wellbore fluid conduit from a position in which it is clear of the tubing hanger/spool interface to a position in which it seals across the tubing hanger/spool interface. Therefore, with the sleeve positioned clear of the tubing hanger/spool interface, the tubing hanger and attached completion tubing may be run or retrieved. As it is capable of sealing across this interface, the sleeve eliminates the need for the relatively bulky annulus seals and their energizing mechanisms above and below the laterally extending wellbore fluid conduit.
This provides the dual benefits of releasing radial space while also making the completion system and in particular its seal-forming surfaces or areas less susceptible to damage. Preferably, the spool is provided with recessed sealing profiles affording protection to the seal areas during drilling operations.
The laterally extending wellbore fluid conduit may be used to contain any fluid that is conventionally conveyed to or from the wellbore via the tubing hanger. Most often in production mode this will be production fluid, but the fluid could also be for example lift gas, injection water or other fluids such as glycol for chemical injection, or fluids for pressure and circulation testing.
The wellhead sealing system of the present invention may provide some or all of the following additional benefits:
1. Reliability under cyclical loading.
2. Ability to be remotely operated using simple tooling.
3. Ability to accommodate 10,000 psi (69 MNmxe2x88x922) nominal maximum working pressure as a base case. However a family of such sealing systems may be produced, also including, for example, members for 5,000 psi (35 MNmxe2x88x922), 15,000 psi (104 MNmxe2x88x922) and other duties as required.
4. Minimum temperature range of 0 to 250xc2x0 F. (xe2x88x9217.8xc2x0 C. to 121xc2x0 C.), and preferably beyond at either end.
These and other objects and advantages of the present invention will be made apparent from the following detailed description, with reference to the accompanying drawings.